1. Field Of The Invention
This invention relates to a kit for conversion of a manually powered wheelchair to one which is driven by power hubs which are integrated into the rear drive wheels. More specifically, this invention provides a unique combination of components both for the mounting and driving of the wheelchair's rear wheels so as to preserve the maneuverability of the chair while at the same time enhancing its stability as a powered conveyance.
2. Description Of The Prior Art
The manually powered wheel chairs in use throughout the world have certain basic physical and functional qualities which are common to all such chairs. Generally, such chairs are, by design, similar in their overall physical dimensions to allow for passage through doorways and share other similar features to allow for their collapse (folding) during transit in a car or other similar vehicle. Other similarities are also apparent in the seat and seat back construction and weight distribution, which permit the occupant to elevate the front wheels to navigate a curb or other obstruction. Generally, the individual confined to a manually powered wheelchair is relatively physically robust and can assist himself (in an emergency) should the circumstances require it.
Unfortunately, the confinement of an individual to a powered wheelchair is generally indicative of an individual's reduced physical strength and/or manual dexterity. Accordingly, such powered chairs must be designed with such an individual in mind and must accommodate increased dependency of the individual on the chair's stability and maneuverability. Moreover, because of such individual's reduced physical, and possibly mental, faculties, the powered chair must also anticipate the effects of a power failure and permit its manual operation without elaborate disengagement of the powered drive wheels from the gear train which connects such wheels to the drive motor.
As is further evident, powered wheelchairs require different design considerations because of the changes in weight distribution and other obvious operational differences. Generally, when an individual is required to use a powered wheelchair, such individual is unable to assist himself even in the most fundamental tasks and, thus, such chairs must, of necessity, be fully operational through the armrest mounted controller; and, upon failure of the power drive, be capable of transition to manual operation without occupant assistance. Thus, the phrase "manually operated wheelchair", as that phrase is used in the description and characterization of the prior art, can be inclusive of both unpowered and powered wheelchairs to the extent that a "powered" wheelchair requires occupant assistance and/or modification (manual disengagement) of the power drive mechanism to effect transition to manual operation in the event of a power failure.
The following patents are representative of the patent literature as related to the adaptation of power drive systems to wheelchairs and similar devices. These patents are listed and discussed in chronological order, based upon their date of issue, and thus no significance is to attach to such order of listing or discussion.
U.S. Pat. No. 3,930,551 (to Cragg) describes a wheelchair (of somewhat unorthodox design) in which an electrically (battery) powered motor is coupled through a driven pinion gear to the rear (drive) wheels of a wheelchair. In the event of power failure, or interruption, the gear train can be manually disengaged by a lever (Ref. No 78) to shift the drive mechanism into "neutral" and thereby allow manual operation (free wheeling) of the drive wheels. Thus, if the occupant is of limited physical capacity, and the power drive fails, the wheelchair will be rendered inoperative, potentially exposing its occupant to needless risk and anxiety.
U.S. Pat. No. 4,436,320 (to Bruderman et al) describes an elaborate powered chassis for use as a wheelchair. In the device described by Patentees, the drive mechanism is integral with the front wheels and is otherwise dedicated to the configuration of the Patentees' chassis (not transferable to more conventional wheelchair designs). In addition to the foregoing apparent limitations, the folding of the chassis is further unique to accommodate its unorthodox construction. Patentees are otherwise silent as to the operation and mechanical design of their drive mechanism; and, it can be assumed that upon its failure, the drive wheels may become locked or resistant to manual movement.
U.S. Pat. No. 4,960,287 (to Lautzenhiser et al) describes an electrically powered wheelchair in which the battery carriage permits "quick release" of the battery to allow for folding and storage during transit of the chair in another conveyance. The electric drive motors are mounted inboard on the frame at somewhat different positions, relative to one another, so as to not change the overall width of the chair and yet minimize interference upon collapse of the frame and folding of the chair (see FIG. 2). Patentees are otherwise silent as to the operation and mechanical design of their drive mechanism; and, it can be assumed that upon its failure, the drive wheels may become locked or resistant to manual movement.
U.S. Pat. No. 4,961,473 (to Jones) describes a kit for conversion of a manually powered wheelchair wherein a pair of power driven rollers engages the existing (unmodified) rear wheels of the converted chair. The motor drive assembly includes a gear train (worm gear) that couples the output shaft of the motor to power transfer rollers. Apparently, the gear train does not allow free wheeling of the chair, in the event of power failure or interruption. and, thus, the Patentee has provided for manual engagement and disengagement of the motor drive assembly from the rear wheels of the chair by means of a lever (Ref. No 60) to permit manual operation of chair.
U.S. Pat. No. 5,161,630 (to Garin et al) describes a motorized wheelchair drive assembly that can be selectively engaged or disengaged by the occupant thereof to permit use of the chair in either the manual or motorized mode. The drive assembly described by the Patentees is mounted on the hub of the rear wheels of the chair; and, the motor thereof is mechanically coupled to the rear wheel by means of a worm gear assembly. The configuration of Patentees' power drive assembly requires the addition of two drive motors (Ref. No. 72), a worm gear (Ref. No 114), supporting structure mounted inboard of the rear wheel (on the chair frame) and a drive hub (Ref. No. 120) outboard of the rear wheel. In order to accommodate and mount all this additional hardware, the chair frame is modified by the addition of a metal plate (Ref. No 124). As is evident from the foregoing, the above power drive assembly changes not only the overall width of the chair but also introduces additional mechanical components which can interfere with collapse and folding of the chair during the transit thereof. In order to disengage the gear train from the drive hub to permit manual operation of the chair in the event of power interruption, the occupant must manually actuate the "U" shaped handles (Ref. No. 146) pivotally mounted on each of such hubs.
As is evident from the foregoing discussion, the adaptation of a power drive assembly to a wheelchair has been beset with a number of subtle mechanical and operational problems. It is clear that in most, if not all instances, the interruption of power to the drive wheels will render the chair inoperative. To the extent the drive wheels can be disengaged to allow for manual operation, such disengagement generally requires physical manipulation of one or more levers or handles to effect such release.
Accordingly, there remains a continuing need for a simple and cost effective power drive assembly for a wheelchair which is both easy to install, does not otherwise adversely alter the handling characteristics of the chair and allows for manual operation of the chair in the event of power interruption, without occupant intervention or manual disengagement of the power drive assembly.